Variation Of Droplet Size Research Articles

Search for Microphysical Signatures of Stochastic Condensation in Marine Boundary Layer Clouds Using Airborne Digital Holography

AbstractDroplet growth due to stochastic condensation has been considered as one of the mechanisms to cause broadening of cloud droplet size distributions and jump the bottleneck between droplet growth due to diffusion and collision‐coalescence. Digital in‐line holography is used to measure variations in droplet number concentration and droplet size in marine boundary layer clouds. Distributions of phase relaxation times are quite broad for some clouds. Turbulence correlation times are estimated, and the comparison of these with phase relaxation times suggests that clouds exist in both fast and slow microphysical regimes. Presumed signatures of stochastic condensation, such as increasing relative size dispersion and increasing droplet size with decreasing number density, are observed.

Superlative behavior of W/O type phytocosmetic formulationâs SPF (solarprotection factor) in response to thixotropic and antioxidant attributes.

The aim of the current research work was to develop a stable herbal cosmetic formulation and to study its rheological characteristic and their impact on solar protection factor (SPF). The formulations possess good antioxidant potential and virtuous sensory attributes. An accelerated stability study was performed under variant thermal conditions for 60 days in order to evaluate any variation in droplet size and thixotropy. The droplet size of fresh formulations F1 (WSEA) and F2 (SNEA) was found to be 2.04 ± 0.577 μm and 2.31 ± 0.532 μm with thixotropic value 16964 ± 41 (D/cm2.s) and 16471 ± 35 (D/cm2.s) respectively. The solar protection factor at optimum thixotropic values of both formulations F1 and F2 was 3.11 ± 0.34 and 2.34 ± 0.12 respectively. At accelerated stability conditions, there was a minute reduction in the formulation consistency due to decrease in viscosity and increase in droplet size. The good SPF in these herbal cosmetic formulations was attributed to the presence of polyphenols, which protect the skin from harmful UV radiations.

Comparative study on foaming and emulsifying properties of different beta-lactoglobulin aggregates.

Different conditions in food processing lead to different aggregates of protein. β-Lactoglobulin nanoparticles (BLGNPs) and fibrils (BLGFs) were prepared by adjusting pH and temperature, and thereby their foaming and emulsifying properties were compared to native globular β-lactoglobulin (NGBLG) at pH 7.0 and pH 4.0. A foam analyser, a microparticle size analyser, an interfacial rheometer and an atomic force microscope (AFM) were used to characterise foaming/emulsifying functionalities and interfacial microstructures/mechanical properties. The foam and emulsion stabilities were assessed by measuring the decay of foam height and the variation of emulsion droplet size, and both were found to be in the order of BLGFs > NGBLG > BLGNPs. Foams were more stable at pH 4.0 while emulsions were more stable at pH 7.0. Surface dilatational modulus (E) of NGBLG and its aggregates at pH 4.0 was greater than that at pH 7.0, with BLGFs showing the highest value of E and thus the highest resistance to membrane damage. The emulsion prepared with NGBLG and its aggregates had more negative charges at pH 7.0 than at pH 4.0. The foaming stability seemed to be more controlled by interfacial elasticity while the emulsion stability was more determined by surface charges. AFM analysis demonstrated different microstructures at the air-water interface between pH 4.0 and 7.0 and among the different protein aggregates, which could well explain their foaming and emulsifying properties.

Atomization characteristics of multi-type aerial nozzles in wind tunnel and low airflow velocity condition in manned agricultural helicopter

In order to explore the atomization characteristics of the LICHENG series nozzle for manned agricultural helicopter under medium and low airflow velocity conditions, droplet size tests on five sizes of nozzles 11002, 11003, 11004, 11006 and 11010 were carried out by laser diffraction device (LDD), based on the high-low speed composite wind tunnel for agricultural aviation designed by the National Center for International Collaboration Research on Precision Agricultural Aviation Pesticides Spraying Technology (NPAAC) of South China Agricultural University (SCAU). The results showed that under the three spray pressures of 30, 40 and 50 psi, the droplet sizes of the five types of nozzles expressed similar trends with the increase of airflow velocity. Among them, the droplet size variation of nozzles 11006 and 11010 with larger orifice size was the most significant, the largest range of D V0.1 was nozzle 11010, and the largest range of D V0.5 and D V0.9 was nozzle 11006. In addition, the changes of spray pressure would directly affect the quality of spray, especially the nozzles 11002, 11003 and 11004 with small orifice sizes were significantly affected. Under the condition of medium and low airflow velocity of 0-27.8 m/s, 89% of spread value (SV) by the five nozzles were in the range of less than 15%, but there were some test nozzles with poor spray stability during the test, which made the measurements of droplet size value larger, resulting in a maximum test deviation of up to 210.9 I¼m. The result also exposed the limitations exist in wind tunnel droplet size testing by using LDD, and an increase in airflow velocity resulted in a larger measurement droplet size. This phenomenon was particularly significant in the D V0.5 test results of various types of nozzles. This study can provide experimental data guidance for the optimization design and parameter selection of aerial nozzle for manned agricultural helicopter. Keywords: manned helicopter, aerial nozzle, wind tunnel, droplet size, agricultural application, spray classification DOI:  10.33440/j.ijpaa.20190201.0031  Citation: Yao W X, Lan Y B, Hoffmann W C,  Guo S, Chen S D, Wen S, et al.  Atomization characteristics of multi-type aerial nozzles in wind tunnel and low airflow velocity condition in manned agricultural helicopter.  Int J Precis Agric Aviat, 2019; 2(1): 9–17.

A Comprehensive Review on Emulsions and Emulsion Stability in Chemical and Energy Industries

AbstractEmulsion refers to a mixture that includes two or more liquid phases. The uses of emulsions are found in several chemical, energy, and environmental industries such as the food, health care, chemical synthesis, and firefighting sectors. Water‐in‐oil emulsions are formed spontaneously during oil production when oil and water are mixed together and in the presence of asphaltene as a naturally occurring surfactant. For operational and economic reasons, oil emulsions need to be treated to recover both oil and water phases. To develop more efficient emulsion treatments, it is essential to have a better understanding of the factors that affect emulsion formation and stability. The droplet size variation is an important parameter that influences the stability and rheological characteristics of the emulsions. In addition, the available interfacial area for any possible chemical reactions might affect the behaviours and properties of the emulsions in various transport phenomena systems. The adequate knowledge of the factors and mechanisms affecting the droplet size and emulsion stability still needs further engineering and research activities. This study is aimed to provide a comprehensive literature review on the formation of water/oil emulsions and their stability in various physical systems (e.g., pipeline networks and porous media). In this review, fundamental aspects of emulsions, emulsion formation mechanisms, analytical models, and numerical solutions for the description and characterization of the behaviours of emulsions in porous media and/or separators are discussed. The effects of different fluid properties, physical model characteristics, and operational conditions on emulsion behaviours are studied. This paper also summarizes the previous experimental and modelling studies and methodologies with a focus on reliable laboratory equipment/tools and simulation and modelling packages/strategies for the investigation of emulsion stability and droplet size distribution where a systematic parametric sensitivity analysis to study various effects of important thermodynamic, process, and medium properties on the targeted variables is conducted. This review manuscript provides useful guidelines to characterize and model emulsions and their behaviours in different industrial sectors, which will considerably help to conduct better design and optimal operation of corresponding equipment.

Plant based Pickering stabilization of emulsions using soluble flaxseed protein and mucilage nano-assemblies

A straightforward and green method of stabilizing emulsions was developed using plant-based particles from complexation of flaxseed protein (FP) and the soluble fraction of flaxseed mucilage (SFM). The extracted SFM was characterized using 1H and 13C NMR. The effect of pH, total concentration (TC) and FP to SFM ratio on the formation of assemblies was investigated by light scattering, surface charge and optical density measurements. The selected negatively charged complex particles had the size of 369.46 nm and near neutral wettability. These nano-assemblies were utilized to fabricate Pickering emulsions. The effect of the FP to SFM ratio, TC and oil content was evaluated on the droplet size of the Pickering emulsions. The droplet size variation of the emulsions stabilized by the selected complex particles and protein only was also monitored during 30 days of storage and the flocculation and coalescence indices were evaluated. On comparing the emulsifying ability of the complex particles with protein particles at pH 3, native FP resulted in poor formation and stability of emulsions due to the aggregation while complex stabilized emulsion was stable with no variation in the droplet size during storage. The microstructure of the emulsions was demonstrated utilizing Cryo-SEM and CLSM. The complexation was able to improve the functionality of FP for emulsion stabilization. The fabricated FP-SFM Pickering emulsions have potential application for the encapsulation of lipophilic bioactive compounds in natural and plant based food, beverage, and pharmaceutical formulations.

Energy analysis of spray flash evaporation from superheated upward jets

Flash evaporation is widely used in desalination technologies. The flash evaporation from upward and downward jets shows different characteristics. To study the upward flash evaporation, a model based upon droplet analysis is developed. The present model takes the droplet motion, droplet size variation and droplet temperature into consideration. The model is validated against the corresponding experimental results from previous literature and the calculated results from the model coincide with the experimental results. The dimensionless temperature profiles of the upward and downward flash evaporation are compared. Employing this model, the influences of the injection pressure, evaporation chamber pressure and flow velocity on the energy utilization efficiency and spray flash speed are investigated. The critical time and critical distance are also compared and analyzed.

The basic investigation of evaporation rate and burning temperature of various type of liquid fuels droplet

The investigation of spray combustion phenomenon in order to improve the combustion efficiency has been conducted through the experimentally or simulation. On the liquid spray combustion phenomenon the size of liquid fuel that was sprayed into the combustion chamber (droplet) is very small, ranging between 1-25 μm. Due to the very small size of liquid droplet, the gravitation effect of liquid droplet was negligible or near the microgravity condition. Therefore, this study was conducted to observe the behaviour of evaporation rate and the burning temperature of various types of liquid fuels droplet. The results of this research can be used as a basis in experiments or modelling of spray combustion. The liquid fuel that was used in this experiment are n-decane, pertamax, pertalite and pertamax turbo. Experiments were performed by injecting liquid fuel into droplets on SiC fiber grids with several variations of droplet size (0.5 mm, 0.75 mm, 1 mm, 1.25 mm and 1.5 mm).The results show that the droplet size of each fuel has a positive correlation to the evaporation rate and also the combustion temperature. This paper will discuss in detail the characteristics of the evaporation rate and the burning temperature of each type of liquid fuels droplet.

Microexplosion and ignition of biodiesel/ethanol blends droplets in oxygenated hot co-flow

Microexplosion and ignition characteristics of biodiesel/ethanol blends were studied by suspending single droplets on fibers in a tubular oven at different ambient conditions. The range of ethanol content in initial fuel, as an important parameter, was changed from 0% to 100%.Heating temperature and gas flow were also reference variables, which were respectively changed from 300 °C to 500 °C and from 0 L/min to 10 L/min. Behaviors of droplet microexplosion and ignition were recorded by high speed camera. Temporal variation of droplet size, time to microexplosion and ignition delay time were all analyzed for every cases. The results showed that microexplosion could be found in most cases due to high volatility distinction of biodiesel and ethanol and be expedited and intensified at fuel for nearly equivalent volume mixing, or at enough high temperature and in a certain gas flow. However, ignition was achieved only in some situations which biodiesel content in initial fuel and temperature was relatively high and gas flow rate was moderate. Further, under the condition that the temperature and flow rate remain unchanged, when the ethanol content reached 50%, the micro-explosion intensity which was named the normalized diameter reaches the maximum (1.3). At the same time, the delay time of micro-explosion is also reduced to the minimum (0.23 s). Under the condition that the ratio and flow rate remained the same, when the ambient temperature rose to 400 °C, the micro-explosion intensity reached the maximum. At this time, the normalized diameter of the mixed droplets approached 1.5. Under the condition that the temperature and ratio remained the same, when the flow rate was 5 L/min, the ignition delay time was the lowest (about 2.8 s), when the flow rate was 10 L/min, the micro-explosion intensity was the largest, and the normalized diameter reached 1.8. Beyond this, it was found that raising the ratio of ethanol in the blended fuel could increase the burning rate but lower the ignitability, and the ignition delay time could be shortened when the droplet exhibited microexplosion and fuel of near equi-volume blends, experiencing the most violent microexplosion, optimized the improvement, which could be found more obviously at high temperature and high speed airflow.

On Which Microphysical Time Scales to Use in Studies of Entrainment‐Mixing Mechanisms in Clouds

AbstractThe commonly used time scales in entrainment‐mixing studies are examined to seek the most appropriate one, based on aircraft observations of cumulus clouds from the RACORO campaign and numerical simulations with the Explicit Mixing Parcel Model. The time scales include the following: τevap, the time for droplet complete evaporation; τphase, the time for saturation ratio deficit (S) to reach 1/e of its initial value; τsatu, the time for S to reach −0.5%; and τreact, the time for complete droplet evaporation or S to reach −0.5%. It is found that the proper time scale to use depends on the specific objectives of entrainment‐mixing studies. First, if the focus is on the variations of liquid water content (LWC) and S, then τreact for saturation, τsatu and τphase are almost equivalently appropriate, because they all represent the rate of dry air reaching saturation or of LWC decrease. Second, if one focuses on the variations of droplet size and number concentration, τreact for complete evaporation and τevap are proper because they characterize how fast droplets evaporate and whether number concentration decreases. Moreover, τreact for complete evaporation and τevap are always positively correlated with homogeneous mixing degree (ψ); thus, the two time scales, especially τevap, are recommended for developing parameterizations. However, ψ and the other time scales can be negatively, positively, or not correlated, depending on the dominant factors of the entrained air (i.e., relative humidity or aerosols). Third, all time scales are proportional to each other under certain microphysical and thermodynamic conditions.

Wetting Behavior of Polymer Droplets: Effects of Droplet Size and Chain Length

Monte Carlo computer simulations were utilized to probe the behavior of homopolymer droplets adsorbed at solid surfaces as a function of the number of chains making up the droplets and varying droplet sizes. The wetting behavior is quantified via the ratio of the perpendicular to the parallel component of the effective radii of gyration of the droplets and is analyzed further in terms of the adsorption behavior of the polymer chains and the monomers that constitute the droplets. This analysis is complemented by an account of the shape of the droplets in terms of the principal moments of the radius of gyration tensor. Single-chain droplets are found to lie flatter and wet the substrate more than chemically identical multichain droplets, which attain a more globular shape and wet the substrate less. The simulation findings are in good agreement with atomic force microscopy experiments. The present investigation illustrates a marked dependence of wetting and adsorption on certain structural arrangements and ...

Droplet Breakup Dynamics in Bi-Layer Bifurcating Microchannel.

Breakup of droplets at bi-layer bifurcating junction in polydimethylsiloxane (PDMS) microchannel has been investigated by experiments and numerical simulation. The pressure drop in bi-layer bifurcating channel was investigated and compared with single-layer bifurcating channel. Daughter droplet size variation generated in bi-layer bifurcating microchannel was analyzed. The correlation was proposed to predict the transition between breakup and non-breakup conditions of droplets in bi-layer bifurcating channel using a phase diagram. In the non-breakup regime, droplets exiting port can be switched via tuning flow resistance by controlling radius of curvature, and or channel height ratio. Compared with single-layer bifurcating junction, 3-D cutting in diagonal direction from bi-layer bifurcating junction induces asymmetric fission to form daughter droplets with distinct sizes while each size has good monodispersity. Lower pressure drop is required in the new microsystem. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation, fission and sorting. The model system can be developed to investigate the encapsulation and release kinetics of emulsion templated particles such as drug encapsulated microcapsules as they flow through complex porous media structures, such as blood capillaries or the porous tissue structures, which feature with bifurcating junctions.

Experimental Study of the Interaction Between Water Sprays and Smoke Layer

This paper concerns the interaction between water sprays and a smoke layer in a corridor, without any interaction with fire activity. Three water sprays are tested, a high-pressure water mist system and two sprinkler systems under different operating pressures. Our study aims to compare the impact of these three sprays on the smoke layer, based on the analysis of temperature and transmittance profiles. Characterization of the smoke layer before spray activation, based on either temperature or transmittance was found to be similar, providing a smoke free layer at around middle height in the corridor. During spray operation, discrepancies were observed in some cases depending on whether the smoke layer was studied based on the temperature or the transmittance profiles. Spray operation may provide gas cooling, resulting in homogeneous temperature profiles, while vertical variations of droplet size and soot or droplet concentration can still induce a variation in transmittance. The impact of water spray on the smoke layer varies with the spray system. For the water mist system and the highest-pressure sprinkler system, the spray operation induces a complete de-stratification with well-mixed steady-state conditions along the corridor as well as strong smoke cooling and visibility alteration. With the lowest-pressure sprinkler system, only a localized alteration of this stratification is observed under the spray, while the environment remains thermally and optically stratified downstream in the corridor despite spray operation. Relationships described in the literature were used to confirm and explain these observations. Ratios were evaluated to compare the drag effect due to the spray and the buoyancy effect related to the fire. All tests provided ratios of drag number over buoyancy number much greater than one. This confirms the ability of these relationships to predict the occurrence of de-stratification. Qualitatively, the highest ratios were found for the high pressure system and for the water mist system, which actually led to the most important de-stratification effects. In contrast, the weaker ratio found for the lower pressure system was still above one, i.e., coherent with a de-stratification which did not affect the whole corridor however.

Shrinking of Rapidly Evaporating Water Microdroplets Reveals their Extreme Supercooling.

The fast evaporative cooling of micrometer-sized water droplets in a vacuum offers the appealing possibility to investigate supercooled water-below the melting point but still a liquid-at temperatures far beyond the state of the art. However, it is challenging to obtain a reliable value of the droplet temperature under such extreme experimental conditions. Here, the observation of morphology-dependent resonances in the Raman scattering from a train of perfectly uniform water droplets allows us to measure the variation in droplet size resulting from evaporative mass losses with an absolute precision of better than 0.2%. This finding proves crucial to an unambiguous determination of the droplet temperature. In particular, we find that a fraction of water droplets with an initial diameter of 6379±12 nm remain liquid down to 230.6±0.6 K. Our results question temperature estimates reported recently for larger supercooled water droplets and provide valuable information on the hydrogen-bond network in liquid water in the hard-to-access deeply supercooled regime.

Modeling of spray flash evaporation based on droplet analysis

To enable a more in-depth understanding of the flash evaporation from the downward jet and extend the research range of spray flash evaporation, a mathematical model based on the diffusion-controlled evaporation model was proposed and developed. The droplet motion, droplet size variation and temperature variation are taken into account in the present model. The model was validated against the experimental data sets from literature sources. The temperature variation against the traveled distance was obtained and analyzed. Four variables, namely, flow velocity, pressure attenuation ratio, droplet size and relative humidity, were investigated by means of this model.

Modeling of n-Hexane and n-Octane liquid fuel jets in gaseous crossflow for evaporation, combustion and breakup evaluation

This paper investigates the phenomena of liquid fuel jets in gaseous crossflow for two types of fuels, namely n-Hexane and n-Octane. In this regard, a numerical model is developed to predict a droplet behavior including trajectory, velocity, evaporation and combustion, size degradation, breakup time and radius of produced child droplets. Therefore, the mass, concentration, energy and momentum conversation equations are derived to evaluate the droplet acceleration from initial conditions. The velocity distribution is then obtained through a numerical integration of the acceleration over time. A further integration is made to determine the droplet position. In addition, evaporation and combustion and Taylor Analogy Breakup (TAB) models are integrated to assess droplet evaporation, combustion rate, and breakup behavior during the injection process. The professional version of the Engineering Equation Solver (EES) software is used to solve the model which has the advantage of providing the thermodynamic properties of the different fluids involved through predefined functions. The behaviors of droplets are investigated for two injection cases: evaporation only and evaporation and combustion. The results obtained are presented in the variations in trajectories, velocities, droplet size and surface temperature corresponding to each case and type of fuel.

Study of variation in droplet size of an aqueous–diesel emulsion formed by an oil-degrading microbial consortium

The variation in droplet size as a function of superficial air velocity (0.2, 0.4 and 0.8 cm s−1) and culture time (10 days) for the biodegradation of diesel by a microbial consortium has been studied in a bubble column bioreactor. With respect to superficial air velocity, the Analysis of Variance ANOVA (at a significance level of α = 0.01) showed that for larger droplet sizes (around 600 nm) the culture time had no influence over the size of the droplets, whereas the air superficial velocity can be accounted as an important factor. However, for smaller droplet sizes (lower than 300 nm) the analysis showed that the culture time had no influence when operating the bioreactor exclusively at air velocities 0.4 and 0.8 cm s−1 but for the case of 0.2 cm s−1 the statistical analysis detected significant differences in the case of culture time. The results indicated that the microbial consortium is needed to produce surfactants, to create oil micro emulsions. This study suggests that a further insight into mass transfer mechanisms, diesel-biodegradation and operating conditions are needed to establish the optimal diesel degradation by microbial consortia in a bubble column bioreactor.

A General Route for Nanoemulsion Synthesis Using Low-Energy Methods at Constant Temperature

The central dogma of nanoemulsion formation using low-energy methods at constant temperature-popularly known as the emulsion inversion point (EIP) method-is that to create O/W nanoemulsions, water should be added to a mixture of an oil and surfactant. Here, we demonstrate that the above order of mixing is not universal and a reverse order of mixing could be superior, depending on the choice of surfactant and liquid phases. We propose a more general methodology to make O/W as well as W/O nanoemulsions by studying the variation of droplet size with the surfactant hydrophilic-lypophilic balance for several model systems. Our analysis shows that surfactant migration from the initial phase to the interface is the critical step for successful nanoemulsion synthesis of both O/W and W/O nanoemulsions. On the basis of our understanding and experimental results, we utilize the reverse order of mixing for two applications: (1) crystallization and formulation of pharmaceutical drugs with faster dissolution rates and (2) synthesis of alginate-based nanogels. The general route provides insights into nanoemulsion formation through low-energy methods and also opens up possibilities that were previously overlooked in the field.

Sprayer Setup Affects Dislodgeable 2,4-D Foliar Residue in Hybrid Bermudagrass Athletic Fields

2,4-dimethylamine salt (2,4-D) is a selective broadleaf herbicide commonly applied to turfgrass systems, including athletic fields, which can dislodge from treated vegetation. Building on previous research confirming 2,4-D dislodgeability is affected by management inputs, field research was initiated in 2014 and 2015 in North Carolina and Tennessee to quantify the effects of sprayer setup on dislodgeable 2,4-D foliar residue from hybrid bermudagrass, which is the most common athletic field playing surface in subtropical and tropical climates. More specifically, research evaluated dislodgeable 2,4-D foliar residue following spray applications (2.1 kg ae ha−1) at varying carrier volumes (187, 374, or 748 L ha−1) and nozzles delivering varying droplet sizes (fine=extended range [XR], coarse=drift guard, or extra coarse=air induction extended range [AIXR]). Overall, data suggest minimal 2,4-D dislodge occurs via soccer ball roll (3.6 m) outside the day of application; however, increasing carrier volume and droplet size can further decrease dislodgeable 2,4-D foliar residue. At 2 d after treatment (DAT), 3.87% of applied 2,4-D dislodged when applied at 187 L ha−1compared to 2.05% at 748 L ha−1. Pooled over data from 1 to 6 DAT, 1.59% of applied 2,4-D dislodged following XR nozzle application compared to 1.13% with AIXR nozzle. While these are small numerical differences, dislodgeable residue was measured via one soccer ball roll, which is a repeated process within the sport and the additive effect of sprayer setup treatments can be employed by turfgrass managers to reduce potential human 2,4-D human exposure.

High performance dye-doped emulsion type PDLC for transmittance variable devices

ABSTRACTPolymer dispersed liquid crystal (PDLC) has been developed for a light shutter due to the advantage of high transmittance. To achieve high transmittance in PDLC's transparent mode and high opacity in shading mode, the black dye-doped emulsion type of PDLC using a membrane filter was investigated with variations in LC droplet size and LC layer thickness. The transmittance difference (ΔT) between the on and off states strongly depended on LC droplet size, and there existed an optimal value to provide higher ΔT, which implies that our method is an effective one for PDLC with a high ΔT.